1. Field of the Invention
This invention relates to coated abrasive articles and a method of making the coated abrasive articles, and, more particularly, to such articles which incorporate an energy curable melt processable binder as the make coat.
2. Description of the Related Art
Coated abrasives generally comprise a flexible backing upon which a binder supports a coating of abrasive particles. The abrasive particles are typically secured to the backing by a first binder, commonly referred to as a make coat. Additionally, the abrasive particles are generally oriented with their longest dimension perpendicular to the backing to provide an optimum cut rate. A second binder, commonly referred to as a size coat, is then applied over the make coat and the abrasive particles to anchor the particles to the backing.
Porous cloth, fabric and textile materials are frequently used as backings for coated abrasive articles. The make coat precursor is typically applied to the backing as a low viscosity material. In this condition, the make coat precursor can infiltrate into the interstices of the porous backing leaving an insufficient coating thickness making it difficult to bond the subsequently applied abrasive particles to the backing and, on curing, resulting in the backing becoming stiff, hard and brittle. As a result, it has become conventional to employ one or more treatment coats, such as a presize, saturant coat, backsize or a subsize coat, to seal the porous backing.
The presize, saturant coat, backsize and subsize coat typically involve thermally curable resinous adhesives, such as phenolic resins, epoxy resins, acrylate resins, acrylic lattices, lattices, urethane resins, glue, starch and combinations thereof. A saturant coat saturates the cloth and fills pores, resulting in a less porous, stiffer cloth with more body. An increase in body provides an increase in strength and durability of the article. A presize coat, which is applied to the front side of the backing, may add bulk to the cloth or may improve adhesion of subsequent coatings. A backsize coat, which is applied to the back side of the backing, i.e., the side opposite that to which the abrasive grains are applied, adds body to the backing and protects the yarns of the cloth from wear. A subsize coat is similar to a saturation coat except that it is applied to a previously treated backing. The drawback of such a presize, saturant coat, backsize and subsize coat is that it entails added processing step(s) which increase the cost and complexity of manufacturing. Similarly, paper backings may be treated to prevent penetration of make adhesives and/or to waterproof.
U.S. Pat. No. 5,436,063 (Follett et al.) describes a coated abrasive article incorporating a make coat which can be readily applied to a porous backing that successfully eliminates the need for a separate presize or saturant coat to seal the backing. The coated abrasive article described in U.S. Pat. No. 5,436,063 generally involves a backing bearing a crosslinked first binder (i.e., a make coat) on the backing, where the first binder consists of an epoxy resin, a polyester component, and a photocatalyst for crosslinking the binder.
U.S. Pat. No. 4,047,903 (Hesse et al.) describes a process for manufacturing coated abrasives and the water resistant coated abrasive products thereof in which the make and size binders are cured by radiation energy. At least one of the make and size binders is a reaction product of either (i) a polycarboxylic acid with an esterified epoxy resin prepared by reacting an epoxy resin with an acrylic acid or methacrylic acid, or mixtures thereof, or (ii) the reaction product of the above-mentioned esterified epoxy resin which is first reacted with diketenes and then reacted with a chelate forming compound.
U.S. Pat. No. 4,547,204 (Caul) describes a coated abrasive in which at least one of the back, base, make, and size layers is an electron beam curable epoxy acrylate or urethane acrylate resin and another layer of which is a thermally curable resin such as a phenolic or an acrylic latex resin. The electron beam curable resin formulation as described can include an epoxy acrylate or urethane acrylate oligomer, a diluent such as vinyl pyrrolidone or multi- or mono-functional acrylates, and a filler with minor amounts of other additives such as surfactants, pigments and suspending agents.
U.S. Pat. No. 4,751,138 (Tumey et al.) describes a radiation curable binder system for coated abrasives where at least one of a saturant, presize, backsize, make, and size coating is formed from a composition curable by electromagnetic radiation involving a photoinitiator portion, and a curable portion containing both ethylenically unsaturated groups and 1,2-epoxide groups, which groups can be supplied by the same or different compounds. The epoxies cure via cationic polymerization and the acrylates cure via free radical polymerization.
U.S. Pat. No. 4,997,717 (Rembold et al.) describes a process of making a coated abrasive and products thereof which involves applying a binder layer to a backing, briefly irradiating the binder layer with actinic light, applying the abrasive particles to the still tacky binder layer before or after irradiation and effecting subsequent or simultaneous heat curing. The binder layer is an epoxy resin used in conjunction with at least one cationic photoinitiator. Additionally a size coat can be utilized.
U.S. Pat. No. 5,256,170 (Harmer et al.) describes a method of making a coated abrasive article where the plurality of abrasive grains are applied to a make coat. The make coat precursor contains at least one ethylenically unsaturated monomer, at least one cationically polymerizable monomer, such as an epoxy monomer, or polyurethane precursor, and an effective amount of a catalyst. The make coat precursor becomes a pressure-sensitive adhesive when partially or fully cured with sufficient tack to hold the abrasive grains during subsequent application and curing of a size coat.
WO 95/11111 (Follett et al.) describes an abrasive article and method for its manufacture in which a make coat layer precursor is laminated onto the front surface of an atypical backing material, such as an open weave cloth, knitted fabric, porous cloth, untreated paper, open or closed cell foams, and nonwovens, to seal the backing surface. A plurality of abrasive particles are adhered to the make coat.
However, a need remains for a multifunctional make coat which not only can seal a porous backing, but which additionally affords enhanced rheological properties to control the amount of resin flow during curing and to reduce the sensitivity to make resin coating thickness, particularly when coating fine mineral grades.